The objective of this project is to define the regulatory signals that control myelination, the event where oligodendrocytes and Schwann cells extend processes that enwrap and ensheath axons. Our search for the molecular basis of transcriptional controls on myelination involves characterization of both the transacting regulatory factors and their cognate cis-acting enhancer/repressor elements necessary for expression of the prototype myelin gene, proteolipid protein (PLP). A combination of biochemical and functional assays have revealed that the essential cis elements are clustered in a small region encompassing the PLP promoter. Regulation of this region most likely requires an interplay of various tissue-specific and ubiquitous binding proteins, some of which directly interact with the cis recognition sequences and some which bind a protein-DNA complex. We have cloned four putative transactivator factors of the former class and identified features of DNA-binding proteins in at least one partially sequenced clone. The isolation of these clones permits a search for the growth factors and other molecules that are critical to the initiation and maintenance of myelin gene transcription. PLP is the most abundant constituent of central nervous system myelin and its loss has devastating effects on myelinating cells. After defining mutations in the proteolipid protein (PLP) gene of a number of animal and human dysmyelinating disorders, we have provided molecular evidence that these mutations act, at least in part, to interrupt oligodendrocyte differentiation. Efforts to identify additional mutations in PLP and in other myelin genes of patients affected with dysmyelinating diseases (such as Pelizaeus Merzbacher) are underway.